He was a pioneer in the field of soil conservation in the United States of America. He founded and headed the Soil Conservation Service, a federal agency now referred to as the Natural Resources Conservation Service. Bennett was born near Wadesboro in Anson County, North Carolina and graduated from the University of North Carolina in 1903. Immediately upon graduation, he became a soil surveyor, and conducted soil studies both in the United States and in other countries that eventually convinced him that soil erosion was a serious problem facing the planet. Bennett was the Inspector for the Southern Division of the United State Department of Agriculture, Bureau of Soils, around 1921. By the 1920s, Bennett was actively writing about soil erosion for popular magazines and scientific journals, with works appearing in publications like Country Gentleman and Scientific Monthly. He co-wrote a United States Department of Agriculture publication in 1928 titled Soil Erosion: A National Menace, which was regarded as his most influential work and garnered the attention of Representative James P. Buchanan of Texas. Buchanan, who was a member of the United States House Committee on Appropriations, helped obtain funding in 1929 for soil erosion studies in the United States. Bennett was also instrumental in the formation of the Soil Conservation Society of America. When the Soil Erosion Service was established as part of the United States Department of the Interior, he became the director in September 1933. He continued to speak out on soil conservation issues, especially through the Dust Bowl years, and eventually influenced the passage of the soil conservation act of April 27, 1935, which created the Soil Conservation Service at the USDA. He remained at the head of that organization until he retired in 1951.
Hammond's efforts changed the mindset of American farmers towards soil conservation, and as director of the Soil Conservation Service helped them learn new ways of cultivation that protected the soil and preserved fertility. The creation of the Soil Conservation Service and its inclusion in the United States Department of Agriculture also marked the US government's acceptance and establishment of the interpretation of soils for soil and water conservation. As director of the SCS Bennett launched a campaign for soil conservation towards educating the public and politicians by identifying areas in the Dust Bowl where the combination of geographic and agricultural systems caused the most serious erosion. Largely in response to Bennett's campaign for soil conservation, Representative James P. Buchanan of Texas attached an amendment to the 1930 appropriations bill authorizing USDA to establish a series of soil erosion experiment stations. The Coon Creek Watershed Project, in southwestern Wisconsin, was the first of many watershed-based projects initiated to demonstrate soil conservation practices to farmers. The locations for these stations were selected by Bennett, and involved teams of researchers establishing plots to measure erosion conditions under various types of crops, soils, rotations, and their responses to different agricultural managements practices and structures. Bennett received many awards and honors for his work during his lifetime, including: President of the Association of American Geographers in 1943, The Frances K. Hutchinson Award from the Garden Club of America in 1944, The Cullum Geographical Medal by the American Geographical Society in 1948, The Distinguished Service Medal by the USDA in 1947. The Audubon Medal by the National Audubon Society in 1947, A fellow of the American Society of Agronomy in 1947. In addition, Bennett was named a charter inductee into the USDA Hall of Heroes in 2000.